Two statements of long ago friends linger in my mind: "I've never been sure what love means" and "It's hard to believe what you once believed when the craziness is gone." In a sense, these thoughts describe why some people remain loveless or continually behave in self-defeating ways. Not from genetics or the mythical "chemical imbalance" which unjustly profits some doctors and corporations but because of early childhood experiences which can deform the human personality into adulthood.
An important goal of childhood maturation is to gain control over feelings, to not behave impulsively as occurs with "road rage." After birth the infant is overwhelmed by feelings, having left the comfort of the womb to enter a booming buzzing world. They do so gradually by assigning positive and negative valences to experiences: positive to those that fulfill their needs and negative to those which ignore them or arouse anxiety.
Most powerful are the negative valences which become associated with angry aggressive behavior and persist, becoming visible during later experiences that produce overwhelming anxiety because of lingering childhood emotional conflict. Though these happenings may be desirable as when seeking intimacy or being assertive on the job.
The unconscious is very powerful and one must respect its power.